The cavity behind the abdominal cavity is called the retroperitoneal space. It contains the kidneys and pancreas, as well as other organs and structures, such as the ureters, aorta, and inferior vena cava. The retroperitoneal space is located behind the peritoneum, which is a membrane that lines the abdominal cavity and surrounds the organs within it. The peritoneum helps to protect and support the organs, and it also allows them to move and function properly within the abdominal cavity.